Question

which of the following is not evidence of a chemical reaction? * a. change in color b. formation of gas c. melting of ice d. formation of a precipitate a chemical equation reads: 2h₂ + o₂ → 2h₂o how many oxygen atoms are in the products? a. 1 b. 2 c. 3 d. 4 what is the correct term for the number placed in front of a molecule to balance an equation? a. subscript b. symbol c. coefficient d. ion

Explanation:

1. A change in color can indicate a chemical reaction as new substances with different color - properties are formed. Formation of gas and formation of a precipitate are also common signs of chemical reactions. Melting of ice is a physical change (solid - to - liquid phase change) and not a chemical reaction.
2. In the chemical equation $2H_2 + O_2

ightarrow2H_2O$, the product is $2H_2O$. Each $H_2O$ molecule has 1 oxygen atom, and since there are 2 $H_2O$ molecules, there are 2 oxygen atoms in the products.

1. The number placed in front of a molecule to balance an equation is called a coefficient. A subscript is a number written below and to the right of a chemical symbol indicating the number of atoms of that element in a molecule. A symbol represents an element, and an ion is an atom or molecule with a net electric charge.

Answer:

1. C. Melting of ice
2. B. 2
3. C. Coefficient